The present invention relates to a releasable anti-ejection device for the control rods of a nuclear reactor.
The mechanisms controlling the control rods of pressurized nuclear reactors are generally located in a pressure-resistant, tight enclosure. The pressure prevailing within this tight enclosure is equal to the pressure prevailing within the reactor, and is consequently several dozen bars.
If for any reason, the seal of such an enclosure is broken, there is a rapid depressurization, leading to a pressure difference between the interior of the enclosure and the interior of the reactor vessel. This pressure difference will lead to a considerable force on the control rods and its controlling mechanism and will have the tendency to eject the control rod from the reactor core.
Thus, pressurized nuclear reactors are equipped with devices for preventing the ejection of control rods, in the case of a depressurization of the enclosure containing the controlling mechanism causing these rods to leave the reactor core.
A large number of anti-ejection devices for nuclear reactor control rods are known. For example, mechanisms of this type are described in U.S. Pat. No. 4,314,882 issued Feb. 9, 1982 as well as in U.S. Pat. No. 3,241,653, filed on Oct. 5th 1971 by the Westinghouse Electric Corporation. Devices of this type comprise a mechanism for controlling the translation of the control rod located in a tight enclosure, integral with the reactor vessel cover, anti-ejection means with respect to the control rod and finally means for controlling the anti-ejection means, which are sensitive to some external cause tending to discharge the control rod from the reactor core.
However, one of the disadvantages of anti-ejection devices of this type is that they do not make it possible for the control rod to be removed from the reactor core when the anti-ejection means remain blocked.